Window insulation
Principle
Whether small openings or large picture windows, windows are generally a prominent feature of a hotel's exterior appearance. They also have significant impact on visual and thermal comfort, and on heating and air conditioning needs.
Windows can be a source of considerable heat loss in winter, while in summer glazed surface can contribute to overheating. Insulated windows are essential to lower heat and air conditioning needs. The type of glazing is an important factor, as well as the type of frame.
Remember that even old "guillotine"-type windows can be doubled-glazed!
(1) To prevent overheating in summer, adequate awnings and window shades are also recommended (see solution no. VIII).
Explanations
What are the appropriate criteria for choosing window glazing?
• The type of window glazing will depend on climate conditions at the hotel's location, the exposure of the facade and noise levels.
• Criteria to be taken into account when choosing glazing are: thermal insulation (to prevent heat loss), thermal emissivity (to benefit from heat gains from sunlight in winter), transmission of natural light (for greater comfort and to reduce the need for artificial lighting), and acoustic protection. The recommended solution is to find the best compromise between all these criteria, considering the hotel's needs.
Glazing properties: Definition
light transmission coefficient: A high light transmission coefficient indicates good transmission of natural daylight
Solar factor/coefficient: heat transmission by solar radiation (2): The heat gain coefficient indicates the proportion of incoming energy that will be transferred through the window glass
Heat gain coefficient (3): A low heat gain coefficient indicates a good level of thermal insulation
Emissivity (4). Low emissivity indicates a low level of energy loss by radiation, and greater comfort in winter
(2) A high solar radiation heat gain coefficient is beneficial in winter, providing heat, but a low heat gain coefficient is preferable in summer to avoid overheating. To resolve this problem it is better to install window glazing with a high radiative heat gain coefficient, combined with awnings and shades to prevent overheating in summer.
(3) The heat transfer coefficient depends on window thickness, on the gas used to fill the space between panes (in double- or triple-glazed windows), and on the emissivity of the glass.
(4) Low-emissivity glass has a thin coating, often metallic, on the inside face of the window that reflects heat radiation and prevents it from radiating from inside to outside through the glass and reducing heat loss.
What are the appropriate criteria for choosing window weather stripping?
• Weather stripping must be carefully chosen because it affects window insulation, weather tightness and indoor ventilation. To ensure well insulated windows, choose window frames with a low heat transfer coefficient.
What precautionary measures should be taken when insulating windows?
• When windows are insulated in an existing building attention must be paid to ventilation needs. A well insulated building will have less natural ventilation, and other ventilation systems will have to be upgraded.
Complete window and French-window installations are eligible for energy savings certificates (ESC) if the surface transmission coefficient is no greater than 2 W/m².K.
The list of all standard energy-saving operations that are eligible for certificates under the ECS scheme can be found on the French ministry website www.developpementdurable.gouv.fr/-Operations-standardisees-.html
Implementation
Whether small openings or large picture windows, windows are generally a prominent feature of a hotel's exterior appearance. They also have significant impact on visual and thermal comfort, and on heating and air conditioning needs.
Windows can be a source of considerable heat loss in winter, while in summer glazed surface can contribute to overheating. Insulated windows are essential to lower heat and air conditioning needs. The type of glazing is an important factor, as well as the type of frame.
Remember that even old "guillotine"-type windows can be doubled-glazed!
(1) To prevent overheating in summer, adequate awnings and window shades are also recommended (see solution no. VIII).
Costs
Replacing single-glazed windows with double glazing generated energy savings on the order of 7%.
The payback time on the new windows is estimated at 9 years.
Preferable performance level under existing thermal regulations, unit by unit Sliding windows Uw 2.6 W/m².C Ug≤ 2 W/m².C
Other windows Uw ≤ 2.3 W/m².C
There are more advanced products on the market today:
• insulating glazing with low Ug coefficient (Ug = 1.0 W/m².C), that cut heat loss in half (cost: 160 to 240 €/m²)
• new double-glazed windows with insulation coefficient Uw = 1.3 W/m².C, which corresponds to glazing insulation coefficient Ug = 1.0 W/m².C and frame coefficient Uf = 1.4 W/m²+.C (Cost on the order of 640 to 960 €/m²)
• triple glazing with insulation coefficient Ug = 0.6 W/m².C
The best windows currently available attain performance of Uw < 1.0 W/m².C Costs and payback times are highly dependent on local conditions and the initial state of the hotel.
Examples
Energy renovation work was done at the Hotel de la Clape (Narbonne Plage), built in 1970, in order to obtain the low-energy building label BBC Renovation (Bâtiment Basse Consommation). Exterior walls were insulated with 15 cm of polystyrene foam, and window frames placed with PVC double-glazed windows.
Double-flow mechanical ventilation was installed, with a 60% efficiency exchanger rating, for indoor air renewal. Heating and cooling are provided by an air/air heat pump. Sanitary hot water is provided by 11.28 m² of solar panels installed on the roof.
A construction programme at the Hotel des Francs (Soissons, Aisne) ensured performance levels that exceed thermal regulations RT2005 requirements by 40%. This was achieved in part by work on windows to reduce building envelope heat losses and heat gain in summer:
• less glazed area
• low-emissivity double glazing
• indoor shades for northern and eastern exposures, outdoor awnings for southern and western exposures.
When the Chartrons Ecolodge (Bordeaux) was renovated, double-glazed low-emissivity windows were installed to reduce heating needs in winter and hold in cool air in the summer.
Benefits
Cost savings
Energy savings:
• Insulated windows hold in heat in winter and coolness in summer, reducing heating and cooling needs.
Potential energy savings for heating: 7% to 15%.
Comfort improvement
Greater comfort in winter:
• Low-emissivity glazing reduces the sensation of "cold windows" in winter, and improves comfort levels for customers.
• Well insulated and weather-tight windows are the best way to eliminate draughts in winter.
Greater comfort in summer:
• Closed and well insulated windows will help keep buildings cool when the outside temperature is higher than indoor temperatures (in combination with awnings and shades).
Greater acoustic comfort:
• Replacing windows is also an excellent opportunity for improving acoustic comfort in your hotel.
Reduced CO2 emissions
• For a hotel of 1,000 m² that uses 77.5 kWh/m² of natural gas heating annually, and applying emission factors for France, a 13% savings in energy consumption represents:
3.15 t CO2 eq of avoided emissions each year
Emission factors for electricity in France: 84.3 g CO2 / kWh.
Emission factors for natural gas in France: 331 g CO2 / kWh (Source: ADEME).
Constraints
Implementation:
• Ease of implementation: Moderate (**).
• Best time for implementation: at the time of facade renovation work.
• Relevant initial situation: the hotel has single-glazed windows, or non-insulting double-glazed windows.